1. Field of the Invention
The present invention is related to encoding and decoding devices suitable for dubbing, and in particular to their handling at the time of occurrence of an uncorrectable symbol error.
2. Related Background Art
Digital VTR, etc., may be taken as an example of a system to record and reproduce image and aural signals.
With the recording and reproducing device of such digital VTR, the analog signals (aural signal and image signal) to be recorded are first converted into digital code, and error correction encoding is executed by the addition of a parity bit for error correction by an error correction encoding circuit (ECC encoding circuit) and recording it on a recording medium. On the other hand, in order to reproduce analog signals from the digital data recorded on the recording medium of the recording and reproducing device, first the digital data are reproduced from the recording medium, the data are input into an error correction decoding circuit (ECC decoding circuit), the symbol errors produced upon recording and reproduction are corrected there as much as possible, error symbols which could not be corrected the by ECC decoding circuit are interpolated (modified) by publicly known method in an interpolation circuit (for example, interpolated by the average value of the preceding and succeeding data), the output of the interpolation circuit is converted into an analog signal, and thus the original signals are reproduced.
In order to execute dubbing of signals digitally recorded on the recording medium as they are in digital mode by using two sets of recording and reproducing units with such construction, the digital data taken out of the interpolation circuit of the recording and reproducing device at one side are entered into the ECC encoding circuit of the other recording and reproducing device at the other side, and the signals are ECC-encoded and recorded in the recording medium. As above, recorded signals can be dubbed as they are in the digital mode, without being reconverted into analog signals.
On the other hand, another method for compression-encoding of image information which has been publicly known is the method like DPCM encoding by midtread type quantifier, wherein the symbols once encoded are decoded into baseband digital signals and then encoded again to obtain the same symbols as before. When such encoding method is employed, deterioration due to encoding occurs only at the time of initial encoding, and even when encoding and decoding are repeated thereafter in digital signals, deterioration does not accumulate and dubbing and editing in the baseband digital signal mode can be executed without accompanying deterioration.
However, in the case of image information, etc., it has been the general practice to modify by interpolation to deal with uncorrectable errors which generated at the time of reproduction of recorded information (upon transmission, in a broad sense) and if thus modified information is encoded again, encoding error generates at that time and it has been a problem. As the result due to the deterioration caused by modifying coupled with deterioration caused by encoding, accumulation of deterioration proceeds as encoding and decoding are repeated.
In addition, also upon reproduction of dubbing data by recording-reproducing device, the dubbed data are reproduced without being identified as to whether they are interpolated data, or correct data and data which are judged to be uncorrectable at the ECC decoding circuit of the recording and reproducing device of the other side may be interpolated by using data recorded after being interpolated at the time of dubbing by the interpolation circuit, and if so, it results in the deterioration of picture quality and sound quality.